Histiocytoid cardiomyopathy (HC), a rare arrhythmogenic disorder, presents as difficult-to-control arrhythmias or sudden death in infants and children, particularly girls. Three cases are described with autopsy findings. In two cases, yellow-tan nodules were grossly visible in the myocardium; in the third case, no gross lesions were identified. Microscopic examination in all three cases revealed multiple, scattered clusters of histiocytoid myocytes which on ultrastructural examination were filled with abnormal mitochondria, scattered lipid droplets, and scanty myofibrils. These pathologic findings are similar to those previously described. The pathogenesis of this entity remains controversial. It was recently proposed that this disorder is X-linked dominant with the associated gene located in the region of Xp22.